The present invention concerns a milling machine for digging trenches in the earth, and more particularly to such a machine of the type comprising at least one substantially vertical support plate, on both sides of which two milling drums are mounted for rotation about an axis substantially perpendicular to the plate.
Already known are such milling machines, generally comprising two plates, which accordingly support four drums, turning two-by-two in opposite directions so as to return the milling debris toward an aspiration intake located at the axis of the machine.
To the extent that such machines are being built with greater and greater capacity, it has been necessary to increase the thickness of the support plate, which must absorb the forces exerted by the earth on the milling drums.
This thickness of the support plate creates difficulties when digging a trench. Indeed, the milling tools mounted on the two drums alongside the support plate must be sufficiently spaced apart from each other to permit the passage of this plate when the drums rotate. The result is the formation of a ridge at the bottom of the trench, whose width is generally at least equal to that of the plate.
When the milling machine descends, the lower edge of the support plate comes against this ridge, and thus can interfere with the progress of the digging.
Various solutions have already been proposed to this problem. Thus, it has been proposed to mount the milling tools alongside the plate movably on the drums, so that the tools of the two drums come close to one another when they are in a position clear of the support plate. However, this solution has proved to be delicate to carry out, to the extent that the axes of articulation of these tools must bear extremely substantial forces.
Another solution was proposed in the document FR-A No. 2 252 011. This solution consists of mounting, on the edge adjacent to the support plate of each of the drums, at least one tool that projects laterally with respect to this edge, the support plate comprising, opposite the trajectory of these tools, circular channels coaxial with the drums in which the ends of these tools pass when the drums turn.
The milling tools are thus mounted fixed on the drums, but the tools that are projecting are able to be spaced apart by a distance less than the thickness of the plate.
This solution has proved to be satisfactory. However, with the thicknesses of the plate now being utilized, the ridge still has a sufficient dimension to resist the weight of the milling machine exerted by means of the lower surfaces of the edge of the support plate.
The object of the present invention is to reduce these difficulties.
For this purpose, the object of the invention is a milling machine for digging trenches in the earth, of the type comprising at least one substantially vertical support plate on both sides of which two milling drums are mounted for rotation about an axis substantially perpendicular to the plate, each of the drums carrying, on that one of its edges that is adjacent to the support plate, at least one tool which projects laterally with respect to this edge, and the support plate comprising, opposite the trajectory of said tools, circular channels coaxial with the drums, in which the ends of these tools pass when the drums turn, characterized by the fact that the projecting tools of one of the drums are disposed at a distance from said axis that is different from the distance to said axis from the tools projecting from the other drum, said channels accordingly having different radii.
The invention therefore allows the ridge to be totally eliminated. Indeed, for this it is sufficient for the bottoms of the two channels to be substantially in the same plane. In fact, it is even possible, by offsetting these planes to make the trajectories of the projecting tools overlap.
The channels can be machined in the support plate, but preferably the support plate is made of cast steel.
In this case, the support plate can present substantially an S shape, when seen in cross-section according to a plane passing through the axis of the drums.
It is also possible, by producing a cast support plate, to easily provide it with fluid intake conduits for the drive motors of the drums, if these latter are disposed in the interior of the drums themselves.